Thanks for reporting this. Your gpl file seems to be separated by spaces, right? JPixelStudio currently only supports tab separated gpl files - try saving it with tabs instead of spaces. The following format usually works:
GIMP Palette
#Palette Name: Ammo-8
#Description: Created by <a target="_blank" href="https://twitter.com/rsvpasap1">rsvp asap</a>.
#Colors: 8
4 12 6 040c06
17 35 24 112318
30 58 41 1e3a29
48 93 66 305d42
77 128 97 4d8061
137 162 87 89a257
190 220 127 bedc7f
238 255 204 eeffcc